# Patent

## Title
Device for coupling out a common-mode signal in a power line communication network

## Abstract

A device for determining a common-mode signal in a power line communication network. The device includes a first line, a second line, and a third line that are connected to a first terminal, to a second terminal, and to a third terminal, respectively. The first, the second, and the third terminal are configured to be connected to a phase line, a neutral line, and a protective ground line of the power line communication network, respectively. The device further includes a common-mode choke configured to couple out the common signal from the first, second, and third line, and the common-mode choke is connected to a termination impedance which is higher than an impedance of the power line communication network.

## Background
An embodiment of the invention relates to a device for determining a common-mode signal in a power line communication network.
BACKGROUND
Power line communication (PLC), also called mains communication, power line transmission or power line telecommunication (PLT), broadband power line (BPL), power band or power line networking (PLN) is a term describing several different systems for using power distribution wires for simultaneous distribution of data. A carrier can communicate voice and data by superimposing an analog signal of the standard 50 or 60 Hz alternating current (AC). For indoor applications, PLC equipment can use household electrical power wiring as a transmission medium. This is a technique used e.g. for home networking or in home automation for remote control of lighting and appliances without installation of additional wiring.
In standard PLC systems the signals are transmitted and received in a differential-mode (DM). Differential-mode signaling is a method of transmitting information over pairs of wires. At DM signaling one wire carries signal and the other wire carries the inverse of the signal, so that the sum of the voltages to ground on the two wires is always assumed to be zero. PLC modems therefore inject a DM signal between a neutral line and a phase line of an outlet of the power line network of the household for communication purposes. Another PLC modem can receive such DM signals at another outlet and use the DM signal for controlling an appliance associated with the receiving PLC modem.
At in-house power line grids, there are asymmetric elements between the phase line and the neutral line, like e.g. an open light switch, a current bar and a fuse cabinet, branches etc. At these asymmetric elements, the DM signals injected by PLC modems are converted to common-mode (CM) signals. Multiple input multiple output (MIMO) PLC modems can use different channels, in particular also common-mode signals, in order to enhance the coverage of PLC systems.
Therefore, there is need for an improved device for a determining a common-mode signal in a power line communication network.
SUMMARY
It is an object of the invention to provide a device for determining a common-mode signal in a power line communication network with an improved ability to detect common-mode signals.
This object is solved via device according to claim 1.
Further details of the invention will become apparent from a consideration of the drawings and ensuing description.



BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS
The accompanying drawings are included to provide a further understanding of embodiments and are incorporated in and constitute a part of this specification. The drawings illustrate embodiments and together with the description serve to explain principles of embodiments. Other embodiments and many of the intended advantages of the embodiments will be readily appreciated, as they become better understood by reference to the following detailed description. The elements of the drawings are not necessarily to scale relative to each other. Like reference numerals designate corresponding similar parts.
FIG. 1 shows a schematic circuit diagram of an embodiment of the invention,
FIG. 2 shows a schematic circuit diagram of a further embodiment of the invention,
FIG. 3 shows a schematic circuit diagram of a further embodiment of the invention,
FIG. 4 shows a schematic circuit diagram of a further embodiment of the invention,
FIG. 5 shows a schematic diagram for explaining the reception of multiple-input multiple-output signals with an embodiment of the invention.



DETAILED DESCRIPTION
In the following, embodiments of the invention are described. It is important to note that all described embodiments in the following may be combined in any way, i.e. there is no limitation that certain described embodiments may not be combined with others. Further, it should be noted that same reference signs throughout the figures denote same or similar elements.
It is to be understood that other embodiments may be utilized and structural or logical changes may be made without departing from the scope of the invention. The following detailed description, therefore, is not to be taken in a limiting sense, and the scope of the present invention is defined by the appended claims.
It is to be understood that the features of the various embodiments described herein may be combined with each other, unless specifically noted otherwise.
In FIG. 1 a schematic circuit diagram of a device 100 for determining a common-mode signal in a power line communication network is depicted. The device 100 might be, for instance, a probe in order to determine common-mode ingress in a DM power line system. The device 100 might be as well a part of a power line modem that receives power line signals.
The device 100 comprises a first line 102, a second line 104 and a third line 106 which are connected to a first terminal 110, to a second terminal 112 and to a third terminal 114, respectively. A phase line P might be connected to the first terminal 110, a neutral line N might be connected to a second terminal 112 and a protective earth line PE might be connected to the third terminal 114.
The device 100 includes a common-mode choke 120 configured to couple out the common-mode signal from the first line 102, the second line 104 and the third line 106.
The common-mode choke 120 is connected to a termination impedance 122 which is higher than an impedance of the power line communication network. The power line communication network comprises all lines and appliances and devices connected to the phase line P, to the neutral line N and to the protective earth line PE.
When using a termination impedance 122 with high impedance, e.g. higher than an impedance of the power line communication network, DM signals transmitted over the phase line P, the neutral line N and the protective earth line PE and, correspondingly, over the first line 102, the second line 104 and the third line 106 are less influenced than by using a termination impedance which is considerably lower, e.g. adapted to an impedance of the power line communication network, e.g. 50 to 150 Ohm.
In FIG. 2 a schematic circuit diagram of a further device 200 for determining a common-mode signal is depicted. The first line 102, the second line 104 and the third line 106 are connected to the first terminal 110, the second terminal 112 and the third terminal 114 by coupling capacitors C, respectively. The coupling capacitor C serves to isolate the device 200 against direct current signal on the phase line P, the neutral line N and the protective earth line PE.
The common-mode choke 120 is wrapped around the first line 102, the second line 104 and a third line 106 and connected to a termination impedance 122 which is higher than the impedance of the power line communication network.
The first line 102 is connected via a first transformer 202 to ground, the second line 104 is connected via a second transformer 204 to ground and the third line 106 is connected via a third transformer 206 to ground. A first output 212 is connected to the first transformer 202 (impedance), a second output 214 is connected to the second transformer 204 (impedance) and a third output 216 is connected to the third transformer 206 (impedance). The first output 212, the second output 214 and the third output 216 are terminated with termination impedances 222, 224, 226, which might have an impedance matching to the impedance of the power line network (e.g. of 50 Ohm), each. The first output 212, the second output 214, and the third output 216 are used to provide the differential-mode signals which are present on the first line 102, the second line 104 and the third line 106.
A fourth output 218 is connected to the common-mode choke 120. The fourth output 218 is configured to provide the common-mode signal present on the first line 102, the second line 104 and the third line 106.
The termination impedance 122 might be realized as an input impedance of an analog-to-digital converter connected to the common-mode choke 120. The input impedance of an analog-to-digital converter might be governed by the gate of a CMOS transistor. The value for such input impedances shall be maximal and can normally be between 1 kΩ and 3 kΩ.
The configuration in FIG. 2 is also known as a star topology. However, it is also possible to use a triangle topology.
In FIG. 3 a further schematic circuit diagram of a further device 300 for determining a common-mode signal is depicted. In the device 300 the determination of the differential-mode signals is performed by a first amplifier 302, a second amplifier 304 and a third amplifier 306.
One of the inputs of the first amplifier 302 the second amplifier 304 and the third amplifier 306 is connected to ground. The other input of the first amplifier 302 is connected to the first line 102 between the common-mode choke 120 and a first impedance 312. The second input of the second amplifier 304 is connected to the second line 104 between the common-mode choke 120 and a second impedance 314. The second input of the third amplifier 306 is connected to the third line 106 between the common-mode choke 120 and a third impedance 316. The outputs of the first amplifier 302, the second amplifier 304 and the third amplifier 306 are connected to the first output 222 to the second output 224 and to the third output 226, respectively.
With these amplifiers it is possible to determine the differential-mode signals on the first line 102, the second line 104 and the third line 106 at the first output 222, the second output 224 and the third output 226. The first amplifier 302, the second amplifier 304 and the third amplifier 306 are arranged in a star topology. However, also in arrangement in a triangle topology is possible.
In FIG. 4 a measurement setup is depicted to determine the influence of the value of the termination impedance 122 to the isolation or divergence of the differential-mode signals on the first line 102, the second line 104 and the third line 106. A generator 400 with a current or voltage source EC and an internal impedance of 50 Ohms further comprises a fourth impedance 402 of 75 Ohm common to the phase line P, the neutral line N and the protective earth line PE and a fifth impedance 404, a sixth impedance 406 and a seventh impedance 407 of 50 Ohm each, wherein the fifth impedance 404 situated is in the phase line P, the sixth impedance 406 is situated in the neutral line N and the seventh impedance 407 is situated in the protective earth line PE. Thus, the generator 400 has an assumed differential-mode impedance of 100 Ohm and a common-mode impedance of 150 Ohm (if the terminal of the protective earth line PE is left open).
A verification with the network analyzer showed that in case the termination impedance 122 is 50 Ohm only, only a small isolation between the signals on the first line 102 and the third line 106 is present. However, the isolation between the differential-mode signals on the different lines 102, 104, 106 is higher, and thus the coupling lower, if the termination impedance is higher, e.g. 1 kΩ or infinite.
In FIG. 5 a schematic diagram showing the feeding possibilities and receiving possibilities in a multiple input multiple output (MIMO) scheme are depicted. A first power line communication modem 500 transmits signals to a second power line communication modem 502 over a power line communication network 504. There are three possibilities for feeding signals into the power line communication network 504.
A differential-mode signal might be fed between the phase line P and the neutral line N, a differential-mode signal might be fed between the phase line P and the protective earth line PE and a differential-mode signal might be fed between the neutral line N and the protective earth line PE. Due to Kirchhoff's laws only two independent paths are possible. It is advisable to use the two best possibilities with respect to e.g. noise properties in order to feed the signals into the power line communication network 504.
On the receiving side there are four possibilities to receive the signals. It is possible to determine the differential-mode signal between phase line and neutral line, to determine the differential-mode signal between phase line P and protective earth PE and to determine the differential-mode signal between the neutral line N and the protective earth line PE. In addition it is possible to detect the common-mode signal CM by using e.g. the common-mode choke 120.
With a proposed device for determining a common-mode signal and a power line communication network there is no longer a lost isolation between the three differential-modes (balanced or symmetrically) between the lines.
Multiple-input multiple-output (MIMO) communication signals are fed or received symmetrically or balanced between the phase line P and the neutral line N, the phase line P and the protective earth line PE and/or the neutral line N and the protective earth line PE. Multiple-input multiple-output technologies show maximum gain compared to signal input signal output schemes if individual signals provide maximum divergence.
With the proposed device a coupling between individual differential-mode signals is reduced, thus increasing the performance of MIMO technology.
Although specific embodiments have been illustrated and described herein, it will be appreciated by those of ordinary skill in the art that a variety of alternate and equivalent implementations may be substituted for the specific embodiments shown described without departing from the scope of the described embodiments. This application is intended to cover any adaptations of variations of the specific embodiments discussed herein. Therefore, it is intended that this invention be limited only by the claims and the equivalence thereof.

## Claims

1. A power line communication (PLC) system comprising:
a PLC network; and
a device operatively connected to the PLC network to couple out a common-mode signal in the PLC network, wherein the device includes:
a first line, a second line and a third line that are connected to a phase line input terminal, to a neutral line input terminal and to a protective earth line input terminal, respectively, the phase line input terminal, the neutral line input terminal, and the protective earth line input terminal, collectively, have a configuration and construction so as to be operatively connected to a phase line, a neutral line, and a protective earth line, respectively, of the PLC network;
a first termination impedance element;
a common-mode choke connected to the first termination impedance element operative to couple out the common-mode signal from the first, second and third lines;
a second termination impedance element coupled in line between ground and a first output;
a third termination impedance element coupled in line between ground and a second output; and
a fourth termination impedance element coupled in line between ground and a third output,
wherein the first termination impedance element has an impedance that is higher than an impedance of the PLC network,
wherein the second, third, and fourth termination impedances match the impedance of the PLC network, and
wherein the first termination impedance is coupled in line between ground and a fourth output, the fourth output being the sole output to output the common-mode signal coupled out by the common-mode choke.

2. The system according to claim 1,
wherein the common-mode choke is wrapped around the first line, the second line and the third line, and
wherein the first, second, and third outputs output differential-mode signals in the first line, the second line and the third line.

3. The system according to claim 1, wherein the first termination impedance element includes an analog-to-digital converter, the impedance of the first termination impedance being represented by an input impedance of the analog-to-digital converter.

4. The system according to claim 1, wherein the impedance of the first termination impedance element is infinity.

5. The system according to claim 1, wherein the device outputs signals based on received common-mode signals and based on differential-mode signals.

6. The system according to claim 5, wherein the device receives the differential-mode signals and the common-mode signals in a multiple-input multiple-out (MIMO)-scheme.

7. The system according to claim 5, further comprising transformers that couple out differential-mode signals.

8. The system according to claim 7, wherein the transformers are arranged in a triangle topology.

9. The system according to claim 7, wherein the transformers are arranged in a star topology.

10. The system according to claim 5, further comprising amplifiers that couple out differential-mode signals.

11. The system according to claim 10, wherein the amplifiers are arranged in a triangle topology.

12. The system according to claim 10, wherein the amplifiers are arranged in a star topology.

13. The system according to claim 1, wherein the device further includes a plurality of coupling capacitors respectively coupled in series with the first line, the second line and the third line between the phase line input, neutral line input, and protective earth line input terminals and the common-mode choke.

14. The system according to claim 1, wherein the device further includes a first transformer, a second transformer and a third transformer having respective first ends connected directly to ground and respective second ends connected to the common-mode choke.

15. The system according to claim 1, wherein said device is a multiple-input multiple-output (MIMO) modem.

16. The system according to claim 1, wherein the impedance of the PLC network is from 50Ω to 150Ω.

17. The stem according to claim 1, wherein the impedance of the first termination impedance element is from 1 kΩ to 3 kΩ.

18. The system according to claim 1, wherein the fourth output is between the first termination impedance element and the common-mode choke.

19. The system according to claim 1, wherein the device further includes:
a first transformer;
a second transformer; and
a third transformer,
wherein each of the first, second and third transformers is connected to the common-mode choke,
wherein the first transformer is connected to the second termination impedance element via the first output,
wherein the second transformer is connected to the third termination impedance element via the second output, and
wherein the third transformer is connected to the fourth termination impedance element via the third output.

20. The system according to claim 19, wherein the device further includes first through third coupling capacitors respectively coupled in series with the first line, the second line and the third line between the phase line input, neutral line input, and protective earth line input terminals and a first side of the common-mode choke,
wherein the first through third transformers are connected to a second side of the common-mode choke.

21. A Power Line Communication (PLC) system comprising:
a PLC network having an impedance; and
a Multiple-Input Multiple-Output (MIMO) PLC modem operatively connected to the PLC network to couple out a common-mode signal in the PLC network, the MIMO PLC modem including:
a first line, a second line and a third line that are connected to a phase line input terminal, to a neutral line input terminal and to a protective earth line input terminal, respectively, the phase line input terminal, the neutral line input terminal, and the protective earth line input terminal, collectively, have a configuration and construction so as to be operatively connected to a phase line, a neutral line, and a protective earth line, respectively, of the PLC network;
a first termination impedance element;
a common-mode choke connected to the first termination impedance element operative to couple out the common-mode signal from the first, second and third lines; and
a plurality of coupling capacitors respectively coupled in series with the first line, the second line and the third line between the phase line input, neutral line input, and protective earth line input terminals and the common-mode choke;
a second termination impedance element coupled between ground and a first output;
a third termination impedance element coupled between ground and a second output; and
a fourth termination impedance element coupled between ground and a third output,
wherein the first termination impedance element has an impedance value higher than the impedance value of the PLC network, and
wherein the second, third, and fourth termination impedances match the impedance value of the PLC network, and
wherein the first termination impedance is coupled between ground and a fourth output, the fourth output being the sole output to output the common-mode signal coupled out by the common-mode choke.

22. The PLC system according to claim 21,
wherein the impedance value of the first termination impedance element is infinity, and
wherein the impedance value of the PLC network is a value selected from the range 50Ω to 150Ω.

23. The PLC system according to claim 21,
wherein the impedance value of the first termination impedance element is a value selected from the range 1 kΩ to 3 kΩ, and
wherein the impedance value of the PLC network is a value selected from the range 50Ω to 150Ω.

24. The PLC modem PLC system according to claim 21, wherein the MIMO PLC modem further includes a first transformer, a second transformer and a third transformer having respective first ends connected directly to ground and respective second ends connected to the common-mode choke.

25. The PLC system according to claim 21, wherein the impedance value of the PLC network is a value selected from the range 50Ω to 150Ω.